Studies have shown that transfer of the human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA into cystic fibrosis (CF) epithelial corrects the defective cAMP-mediated chloride (CI-) transport that characterizes CF. However, no long term approach to somatic cell gene transfer has been developed. Gene transfer with integrating vectors such as retrovirus offers the exciting potential to provide long term correction. However, studies to date suggest that gene transfer with Moloney murine leukemia virus (MMLV) based vectors is inefficient in differentiated airway epithelia, in part because of the low rates of proliferation. Our recent demonstrate that we can overcome the limitation of low rates of cell division by stimulating cells with growth factors that cause differentiated epithelia to divide. Another limitation is the apparent lack of accessible receptors on the apical surface. We found that cells stimulated to divide with growth factors can be readily infected by applying the vector to the basolateral surface or by apply vector to the apical surface when tight junctions are transiently opened by Va/2+ chelation. An exciting recent development is the hybrid lentivirus-based vectors that can infect non- dividing cells. Our preliminary studies show these vectors share the same problem as MMLV with access to receptors from the apical surface. It is not yet clear if lentiviral vectors will be useful for gene transfer to airway epithelia. Now with this preliminary data and these insights into airway epithelial cell biology, we have the tools and reagents to address several important questions. In specific aims we will answer 3 questions: 1) Does infection of dividing cells with integrating vectors produce persistent expression and correction of the CF defect?, 2) Can an integrating vector target non-dividing cells and produce persistent expression and correction of the CF defect? 3) Can integrating vectors correct the CF defect in differentiated epithelia in vivo? The results from these studies are relevant to future work with any integrating vector.